Antiresonant-like behavior in carrier-envelope-phase-sensitive sub-optical-cycle photoemission from plasmonic nanoantennas

Abstract

Optical-field-driven photoemission occurs when the electric field of an optical pulse bends the potential barrier of a material surface such that electron tunneling occurs before the field reverses polarity. At the surface of nanoscale structures, such as ultra-sharp nanoscale tips or metallic nanoantennas, the electric fields of ultrafast optical pulses are strongly enhanced. These enhanced fields can drive optical-field photoemission (i.e. optical-tunneling) and thereby generate and control electrical currents at frequencies exceeding 100 THz 1-11 . A hallmark of such optical-field photoemission is sensitivity of the total emitted current to the carrier-envelope phase (CEP) of the driving optical pulse, and this CEP-sensitivity has been studied using both atomic and solid-state systems 1-3,7,11-17 . Given the quasi-static nature of optical-field emission and the nontrivial dependence of the emission rate on the instantaneous electric field strength, the CEP-sensitive component of the emitted photocurrent is highly sensitive to the energy of the optical pulse, and should carry information about the underlying sub-cycle dynamics of electron emission. Here we examine CEP-sensitive photoemission from plasmonic gold nanoantennas excited with few-cycle optical pulses of increasing energy. We observe antiresonance-like features in the CEP-sensitive photocurrent; specifically, at a critical pulse energy, we observe a sharp dip in the magnitude of the CEP-sensitive photocurrent accompanied by a sudden shift of -radians in the phase of the

Nanoantenna Design for Enhanced Carrier-Envelope-Phase Sensitivity

“…Using plasmonic nanoantennas, the incident optical fields can be enhanced across a broad bandwidth near the structure's plasmonic resonance, allowing for optical-field photoemission to be achieved using much lower incident optical pulse energies. Recent studies have demonstrated that by driving such nanoantennas with few-cycle optical pulses, an appreciable CEP-sensitive photocurrent can be generated using only picojoules of energy at repetition rates approaching 100 MHz [6,7,8,9]. With proper engineering, such nanoantenna-enhanced photodetectors could lead to compact and integratable CEP-sensitive detectors that provide shot-to-shot CEP stabilization and control for compact frequency combs and few-cycle optical sources [10].…”